In the manufacture of multi-layer ceramic (MLC) substrates for integrated circuit semi-conductor package structures, a plurality of ceramic green sheets are formed by doctor blading a slurry containing a resin binder, a particulate ceramic material, solvents and a plasticizer, drying the doctor bladed sheet and cutting it into appropriate smaller sized sheets. Via holes are then punched for forming electrical interconnections through the sheet, electrically conductive paste is deposited in the holes and in appropriate patterns on the surface of the sheets, the sheets are stacked and subsequently fired at a sintering temperature. The punching of via holes in a ceramic sheet presents formidable engineering problems in view of their small size and density. It is conventional to punch via holes with apparatus of the type disclosed in IBM TDB Vol. 13 No. 9, Feb. 19, 1971 P. 2536 or IBM TDB Vol. 16 No. 12, May 1974, P. 3933. In these apparatus a plurality of punch elements arranged in a grid are indexed over the green sheet which is covered by an interposer mask. The interposer mask contains openings where holes are desired to be punched. When a punch element contacts the interposer mask as the punch head is moved downwardly, a hole will be punched where the openings occur since the punch element will pass through the opening in the interposer mask and through the green ceramic sheet. In other areas covered by the interposer mask, i.e., where holes are not desired, the interposer mask will cause the punch element to be retracted into the head.
Such apparatus, while capable of punching complex hole patterns in green sheets, have disadvantages. The interposer mask necessary for operation is relatively expensive to form, it wears out in time since the carbide punches necessary for resisting wear in punching the ceramic expose the mask to significant wear. Further, variation in the MLC product model and design require a large inventory of masks in order to form the necessary patterns, and the extended time necessary for forming interposer masks reduces the capability of the system for making rapid changes.
Automated punch apparatus which utilize individually programmable punches have been suggested in IBM TDB Vol. 20 No. 4, September 1977, P. 1379. This type of punching apparatus does not require the aforedescribed interposer mask, since the individual punching elements can be activated electrically upon command. However, significant cooling problems have been encountered. The punch elements, which are activated by a solenoid, must be positioned close together in order to limit the area in which the punch head must be indexed over. The solenoids generate a very significant amount of heat since one coil in each solenoid is always on. The upper temperature operating limit in such an apparatus is relatively low because parts of the solenoids contain organic insulating material and the like which melts at relatively low temperatures. In view of the high density of heat generated, air cooling is not sufficient to dissipate the heat. It has been determined that liquid cooling is required. The necessity for closely spaced solenoids prohibits the machining or casting of a manifold with the conventional cooling fluid passages. Further, the limited space left between the solenoid elements is insufficient for any significant number of fluid passages and connections. Further, the punch head must be capable of disassembly in order to replace punch elements which wear out and/or break due to the abraisive nature of the ceramic green sheet material. Routine maintenance requirements dictate that the element should be readily disassembled without the need for disconnecting many conduits used for cooling.